Work machines such as, for example, excavators, dozers, loaders, motor graders, and other types of heavy machinery typically use one or more hydraulic actuators to accomplish a variety of tasks. The actuators are fluidly connected to one or more pumps that provide pressurized fluid to chambers within the actuators. An electro-hydraulic valve arrangement is typically connected between the pumps and the actuators to control a flow rate and direction of pressurized fluid to and from the chambers of the actuators.
The electro-hydraulic valve arrangements often include either single-valve or multi-valve arrangements. Single-valve arrangements typically include a valve having only two positions with fixed flow areas to direct flow into and out of the chambers. Single-valve arrangements may also include a bypass orifice, which directs fluid flow from the pump to a reservoir to provide a desired feedback to an operator.
Operator feedback may occur, for example, during a resistive movement of the actuator, when the load on the actuator increases, e.g., when a work implement transitions from soft soil to hard soil. A resistive movement of the actuator increases the pressure within the hydraulic system which causes an increase in fluid flow through the bypass orifice to the reservoir. As such, an operator may sense a slower movement of the actuator and/or a machine component, may sense the need to further actuate a control lever to move an associated component, may sense a change in engine speed, and/or may sense a variety of other operational changes. Such a feedback provided to an operator may be indicative of the load acting on the actuator. Additionally, the bypass orifice acts to limit the pressure within the hydraulic system by relieving pressure increases within the hydraulic system to the reservoir. As such, a particular bypass orifice will limit the pressure available to move the actuator.
Multi-valve arrangements provide increased flexibility over single-valve arrangements by allowing independent control of fluid into and out of each chamber of an actuator. Multi-valve arrangements may not, however, include bypass orifices and thus may adversely affect feedback to an operator and/or may not provide hydraulic system pressure limits during work machine operation.
U.S. Pat. No. 5,540,049 (“the '049 patent”) issued to Lunzman discloses a control system and method for a hydraulic actuator. The '049 patent includes a hydraulic system having a variable flow hydraulic pump delivering fluid under pressure to the hydraulic actuator. The '049 patent also includes a closed center valve that operates to control a flow of the hydraulic fluid to the hydraulic actuator and a separate bypass valve that operates to control a flow of the hydraulic fluid to a fluid reservoir. The '049 patent also includes a control system having a pump controller and a separate bypass controller. The separate bypass controller calculates the effect of the closed center valve stroke signal and derives a signal based on either a pressure modulation or velocity modulation mode to control the position of the separate bypass valve. The separate bypass controller also communicates a signal to the pump controller which controls the output of the pump based on the communicated signal and a pump pressure signal.
Although the '049 patent may include a separate bypass valve to control the flow of pressurized fluid to a reservoir, it may control the output of the pump to achieve the desired output pressure as a function of the desired modulation pressure determined by the bypass controller. Also, during multi-function operations in a pressure modulation mode, the '049 patent may control the output of the pump by summing the multiple modulation pressures to establish a combined modulation pressure, establishing a high pressure limit for the hydraulic system. The '049 patent may also require a complex pump and valve control system to control the pump output.
The present disclosure is directed to overcoming one or more of the problems set forth above.